Magnetic studies of iron(III) nanoparticles in alginate polymer for drug delivery applications P.V. Finotelli a , M.A. Morales b , M.H. Rocha-Lea ˜o c , E.M. Baggio-Saitovitch b , A.M. Rossi b, * a Universidade Federal do Rio de Janeiro, Instituto de Quı ´mica, 21949-900, RJ, Brazil b Centro Brasileiro de Pesquisas Fı ´sicas, Rua Dr. Xavier Sigaud 150, 22290-180, RJ, Brazil c Universidade Federal do Rio de Janeiro, Escola de Quı ´mica, 21949-900, RJ, Brazil Available online 13 October 2004 Abstract Isolated iron ions and iron oxide nanoparticles entrapped in alginate microspheres were studied by 57 Fe Mfssbauer spectroscopy (MS), electron paramagnetic resonance (EPR) and magnetization measurements. Ferric alginate beads were prepared by dropping sodium alginate solution into ferric chloride solution (0.1 and 0.5 M) with stirring under Ar atmosphere. MS and EPR spectroscopy show that iron is absorbed in alginate as Fe(III). The EPR suggests that isolated Fe(III) substitutes sodium in the polymeric structure (narrow line paramagnetic species at g=4.23). This mechanism induces the linking of the alginate units and the formation of the alginate microspheres. During this process, superparamagnetic iron hydroxide particles (broad line species at g =2.22) are precipitated inside the polymer network. MS measurements performed in diluted and concentrated Fe(III) samples displays a paramagnetic doublet at 300 K, and two components at 4.2 K due to a paramagnetic site and blocked superparamagnetic particles. D 2004 Published by Elsevier B.V. Keywords: Alginate; Iron oxide hydroxide; Nanoparticles; Electron paramagnetic resonance; Mfssbauer spectroscopy 1. Introduction Alginate is a linear copolymer composed of 1–4-linked h-d-mannuronic acid (M) and its c -5-epimer a-l-guluronic acid (G), that vary in amount and sequential distribution along the polymer chain depending on the source of the alginate. Soluble sodium alginate can be cross-linked by divalent cations leading to gel formation [1,2]. It has widespread applications in the food, drinks, pharmaceutical and bioengineering industries. Recently, it has been proposed as biomaterial for drug delivery system in which the drug release rates would be activated by external stimuli [3,4]. This activation could be induced by interaction of an external magnetic field with nanostructured magnetic particles previously nucleated in the interior of the alginate. Two main aspects should be known in order to control the biopolymer release rates: (i) the magnetic response of nanoparticles and (ii) mechanical properties of the polymer matrix. Thus, the development of preparation method- ologies of magnetic nanoparticles with controlled dimen- sions is very important for the success of medical applications. Many studies were performed using divalent ions such as Ca 2+ , Sr 2+ , Ba 2+ , to cross-link guluronic acids units of alginate [5], but the way alginate interacts with Fe 3+ is not yet well understood. In addition, because the samples were prepared in an aqueous medium, small iron oxide particle will be nucleated between the alginate polymer chains. Depending on their size and magnetic type, these particles could be in the superparamagnetic state. It has been considered that the alginate polymeric backbone is more conformationally restricted and hence would result in aggregation of iron [6]. Sreeram et al. [6] achieved that the Fe(III) ions are bound to the binding sites in the 0928-4931/$ - see front matter D 2004 Published by Elsevier B.V. doi:10.1016/j.msec.2004.08.005 * Corresponding author. Tel.: +55 21 25867370. E-mail address: rossi@cbpf.br (A.M. Rossi). Materials Science and Engineering C 24 (2004) 625 – 629 www.elsevier.com/locate/msec